Make AI overview Shift+Enter hint smaller and right-aligned

Per reviewer spec: font-size 12px (was 0.8em), margin 0 (was
0.375rem 0 0 0.75rem), and text-align: right so the hint sits under
the send-button side. Muted look (opacity 0.6, line-height 1.4) and
the touch-hide capability query are unchanged.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RCRKyC4sroy5Xk144DGJdS

Author: claude

src/blocks/ai-overview/style.scss

@@ -112,9 +112,10 @@
 // Small muted helper text directly under the input (e.g. "Shift + Enter で改行").
 // Muted via opacity so it inherits and adapts to any theme's text color.
 :where(.hamelp-ai-overview__hint) {
-	margin: 0.375rem 0 0 0.75rem;
-	font-size: 0.8em;
+	margin: 0;
+	font-size: 12px;
 	line-height: 1.4;
+	text-align: right;
 	opacity: 0.6;
 }